Innate Immunity vs. Acquired Immunity

Immunity is defined as the resistance offered by the host against microorganisms or any other foreign substance(s). Immunity can be broadly classified into two types based on its specificity; less specific innate immunity, which is present right from birth, and more specific acquired or adaptive immunity acquired during life.

Innate Immunity

Innate immunity provides the first line of defense against infection. The cellular and molecular components of innate immunity are uniform to all species and are present before the onset of infections. The innate immune system is not specific to particular pathogens, and it recognizes molecular structures unique to microbes called pathogen-associated molecular patterns (PAMPs) via pattern recognition receptors (PRR). The innate immune system aims to eliminate microbes and other foreign particles using:

  1. Physical barriers such as skins 
  2. Proteins (complement)
  3. Phagocytic cells (neutrophils, macrophages)
  4. Antimicrobial compounds synthesized by host cells 

In general, our innate immune system clears most of the microorganisms before they activate the adaptive immune system. 

Adaptive Immunity

When pathogens breach or resist the innate immune system, specific and more robust adaptive immunity comes into play to clear such pathogens. Generally, an adaptive immune response against infection is seen after 5 to 6 days of exposure to a particular antigen. Adaptive immunity is capable of recognizing and selectively eliminating specific foreign microorganisms. Unlike innate immune responses, adaptive immune responses are not the same in all members of a species. Adaptive immunity displays four characteristics attributes:

Antigenic specificity

Adaptive immunity responds to the challenge with high specificity and the remarkable property of “memory.”  Cells or components of the adaptive immune system can distinguish subtle differences among antigens. For example, antibodies can distinguish between two protein molecules that differ in only a single amino acid.


The immune system can generate tremendous diversity in its recognition molecules, allowing it to recognize billions of unique structures on foreign antigens.

Immunologic memory

Exposure to the same antigen in the future results in a quicker and more robust immune response because of immunological memory. Because of immunologic memory, the secondary immune response is quicker and heightened than the primary immune response, and there is a life-long memory against many infections such as measles.

Self/nonself recognition

The adaptive immune system typically responds only to foreign antigens, indicating that it is capable of self/nonself recognition. There are two types of adaptive immune responses, humoral or antibody-mediated immunity, and cell-mediated immunity.

Differences between Innate Immunity and Acquired (adaptive) Immunity

Some of the major differences between Innate Immunity and Adaptive Immunity are summarized in the table below.

 Innate Immunity Adaptive/Acquired  Immunity
DefinitionInnate immunity is the inborn resistance against infections that an individual possesses right from birth due to his genetic or constitutional markup.Acquired immunity is the resistance to infecting foreign substances that an individual acquires or adapts during life.
OriginPrior exposure to the antigen is not required. It is present before the first exposure to microbial antigen.Develops during the lifetime  following the antigenic exposure
ActivityAlways presentNormally silent but triggers after exposure to pathogens
DiversityDiversity is limited; It is active only against a limited repertoire of antigens.Adaptive immunity is more varied and involves specialized immune responses.
SpecificityNon-specific defends against any pathogen upon first exposureAntigen specific-responds to specific pathogen on 2nd or latter exposure
Functional againstGeneral microbes (bacteria, fungi, parasites), etc., Chemical irritants, burns, tissue injury, etc.Microbes, as well as nonmicrobial substances, called antigens
Response timeThe immune response occurs in minutes Takes days to generate an immune response
PotencyIt  has a limited and lower potencyIt has a highly potent  immune response
Target  Antigens Innate immunity develops against antigens that many microbes share (pathogens-associated molecular patterns, PAMPs).Acquired immunity develops against antigens that are specific for each microbe.
Host Cell ReceptorsHost cell receptors of innate immunity (called pattern recognition receptors) are non-specific, e.g., Toll-like receptors.Host cell receptors are specific, e.g., T cell receptor and B cell immunoglobulin receptor.
Immunological MemoryAbsent

It reacts with equal potency upon repeated exposure to the same pathogen.

The presence of memory cells triggers a faster and more potent response when re-exposed to the same pathogen.
HeritanceInnate immunity is inheritablePassive acquired immunity is heritable from mother to neonates for a brief period after birth.
  • Anatomical /physiological barriers like skin, mucous membrane, temperature, pH, chemicals cells
  • Phagocytes (monocytes, macrophages, neutrophils), natural killer cells
  • Complement (alternative & MBL) pathway
  • Normal resident flora etc.


  1. Review of Medical Microbiology and Immunology, Warren E. Levinson, 15th edition
  2. Kuby Immunology, 8th Edition
  3. Roitt’s Essential Immunology, 13th Edition

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

3 thoughts on “Innate Immunity vs. Acquired Immunity

  1. How can I understand systematic bacteriology am reading am not understanding the topic,

  2. Awesome and interesting content. I am trying to read differences between innate and acquired immunity, the whole page is not visible due to other web content. Please help I am a MBChB student from South Africa

    1. Thank you, zesipho. Can you please send us screenshot at or detail information about the problem. We will try to fix it as soon as possible.

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